DESCRIPTION (Adapted from the Applican'ts Abstrcat): Leishmania parasites continue to be important human pathogens, infecting 10-20 million persons worldwide. The important pathogenic features of these parasites are that they only productively parasitize the macrophages of their vertebrate host, and that they are able to survive and replicate in the macrophages phagolysosomes as amastigotes. The amastigotes' extraordinary ability to live in the hostile phagolysosome is essential for their pathogenesis. The PI's research involves identifying the important characteristics of virulent amastigotes. This approach could lead to an understanding of the survival strategy of amastigotes and the discovery of new targets for the therapeutic control of the infectious agent. To this end, they have identified that calcium homeostasis in Leishmania appears to have some unique characteristics not observed in the mammalian host, including the presence of an important amount of Ca2+ stored in acidic vacuoles (acidocalcisomes). In addition, virulent amastigotes have a higher amount of releasable Ca2+ than promastigotes and an increase in their intracellular Ca2+ concentration is an important signal for invasion of macrophages. A gene (lmaa1) for a Ca2+-ATPase (Lmaa1) was cloned and sequenced, and shown to be overexpressed in virulent amastigotes. Our hypothesis is that the acidic compartment that stores Ca2+ present in these parasites may be involved in invasion and intracellular proliferation of amastigotes and could be a useful target for the development of new therapeutic agents. The specific aims of the proposal are to: 1) Investigates whether Lmaa1 localizes to the acidocalcisomes or whether a different CA2+-ATPase is present in these organelles, 2) Investigate the role of lmaa1 in Ca2+ homeostasis and in the processes of invasion, intracellular survival and replication of amastigotes in macrophages. Achieving these goals will form the basis for further study in delineating the importance of Ca2+ homeostasis in the pathogenesis of Leishmanaia infection.